In an existing permanent magnet synchronous motor, it is necessary to provide a temperature sensor to monitor a temperature of the motor. Different permanent magnet materials have different temperature characteristics, and in general, magnetic field intensity of a permanent magnet weakens linearly as temperature increases, and enhances linearly as the temperature decreases. The magnetic field intensity of the permanent magnet always changes linearly in a certain range of the temperature. However, the magnetic field intensity of the permanent magnet reduces sharply and even the permanent magnet loses magnetism in a case that the temperature is exceed a critical temperature (also referred to as the Curie temperature). This process is irreversible, that is, the magnetic field intensity of the permanent magnet will not recover even if the temperature is reduced to be lower than the Curie temperature, and the permanent magnet has suffered irreversible damage, which is the reason for monitoring a temperature of a permanent magnet in a rotor of the permanent magnet motor in a real-time manner, in order to protect the rotor of the permanent magnet motor. The objective of monitoring the temperature of the motor is to, in a first aspect, protect the permanent magnet from losing magnetism due to a high temperature of the motor, and in a second aspect, derive a change in magnetic linkage of the permanent magnet, so as to correct torque output of the permanent magnet motor by compensating a magnetic linkage parameter of the permanent magnet.
However, some problems are caused by the temperature sensor installed in the existing permanent magnet synchronous motor. That is, by using a dedicated temperature sensor, not only system cost is increased, but also system fault points are added, which decreases the system reliability.
In addition, the temperature sensor can be installed only in a stator core of the permanent magnet motor, and there is time delay of thermal conduction between the rotor and the stator core. Therefore, protection for the permanent magnet and compensation for the magnetic linkage parameter cannot be timely and accurate.